Imma Perfetto
Cosmos science journalist
Deep in the tree hollows, logs, and rock cavities on a mountain on the Hawaiian island of Oʻahu, there dwells a macabre caterpillar – with a penchant for body parts.
This rare carnivorous caterpillar skulks about on cobwebs and feasts upon any weakened or recently deceased insects trapped there.
It employs a morbid kind of camouflage to remain hidden from its spider landlord, decorating its portable larval home with the body parts harvested from its meals.
“We have identified body parts belonging to more than 6 different families of insect attached to the silk caterpillar cases,” write the authors of a new study describing the new species in the journal Science.
The “bone collector” caterpillars are very particular about their adornments.
“Body parts are carefully measured for size before the caterpillar weaves them into its collection,” the authors write in the paper.
“Each prospective new addition is rotated and probed …several times, and parts that are too large are chewed down to a size that will fit its case.
And, in captivity when denied access to insect body parts, the caterpillar will not accept just any other piece of detritus as an alternative.
According to the researchers, this suggests that “they recognise and exclusively use corpses in nature and that this decoration is important to their survival.”
“Given the context, it is possible that the array of partially consumed body parts and shed spider skins covering the case forms effective camouflage from a spider landlord,” they write.
Carnivorous caterpillars are extremely rare, making up less than 0.13% of the nearly 200,000 moth and butterfly species in the order Lepidoptera.
“Although caterpillars and spiders are common in the same environments all over the world, only this single caterpillar lineage in Hawaii is known to have made the leap to spider cohabitation,” the authors write.
The bone collector caterpillars are part of the genus Hyposmocoma, an ancient and diverse group of moths found only in Hawaii.
“Phylogenomic analysis shows that the bone collector lineage is at least 6 million years old, [more than] 3 million years older than the island of Oʻahu,” the authors write.
“This suggests that the bone collector lineage once occurred on older islands such as Kauaʻi or Nihoa, from which an ancestor dispersed to Oʻahu.”
But the species has since disappeared from those islands and, after more than 2 decades of searching, only 62 individuals have been found within just 15 square kilometres.
The researchers suggest that species’ extreme rarity and confinement to a single location make it susceptible to many of the same threats – including invasive predators and habitat loss – that are driving other native Hawaiian insects toward extinction.
“Without conservation attention, it is likely that the last living representative of this lineage of carnivorous, body part–collecting caterpillars that has adapted to a precarious existence among spider webs will disappear,” they warn.
